As it is known, the decay of building materials such as marble, stones, tiles, cement and articles manufactured from such materials is caused by chemical and physical phenomena, both of them occurring in the presence of water.
The physical phenomenon acting on all the building materials is the one which is due to the succession of frost and thaw of the water absorbed in the porosity of the material. This involves variations of specific volume and tension capable of causing fractures or in any case disaggregation among the individual particles which compose the material.
Another chemical-physical phenomenon is the dissolution in water of limestone which is present in the marbles as an essential component and in the stones as a binder, with consequent loss of cohesion of the granules.
Still more important for the decay of the materials and of the articles exposed in the open air is the complex of chemical phenomena. They essentially consist in the aggression of the carbonated parts of the material or article by the agents and pollutants which are present in the air (carbon dioxide, sulphur dioxide, nitrogen oxides, hydrochloric acid, hydrosulphurous acid). Such pollutants react with the material in the presence of water and their concentration is particularly high when rain begins.
It is known too that to eliminate or at least to appreciably reduce the above-mentioned drawbacks, it is necessary to sensibly reduce the penetration speed of the water from outside into the material to be protected.
To achieve this purpose, chemical water-repellent compounds are usually applied onto the outside surface of the material to be protected.
U.S. Pat. No. 4,499,146 describes the use, to this purpose, of neutral perfluoropolyethers, i.e. free from functional groups. European patent application nos. 192,493 and 215,492 describe the use of perfluoropolyethers, an end group or both end groups of which consists/consist of functional groups, such as aminic or estereal groups. The same European patent applications describe also the use of functionalized perfluoropolyethers in admixture with perfluoropolyethers having no functional groups, always in chlorofluorocarbon solution.
European patent application no. 89/106,150 has provided a considerable improvement of the application performances and of the applicative technologies thanks to the use of PFPE-based aqueous emulsions or microemulsions, which eliminate the utilization of chlorofluorocarbon solvents.
The use of these emulsions or microemulsions based on functionalized or not functionalized perfluoropolyethers provides good results for protection of marble and synthetic or natural stones having low and mean porosity. Less satisfactory results are obtained with high porosity materials, i.e. materials having a 20-40% or more of porosity.
The above references are hereby incorporated by reference.